iStockphoto/Thinkstock(NEW YORK) -- Bolting from home is a familiar phenomenon for many families who have children with autism, but a new study now suggests these episodes happen more frequently than previously thought.

Nearly half the children who have an autism spectrum disorder (ASD) run away from home, and more than half of those who do go missing long enough to cause concern, according to a new study published Monday in the journal Pediatrics.

Families of more than 1,200 children with autism and more than 1,000 siblings without autism were surveyed online about their children's wandering habits.

Nearly half the families reported that their autistic child had attempted to escape or bolt from home at least once after age 4, compared with only 13 percent of siblings without autism. More than a quarter of the children with autism who left their home were in danger of drowning and 65 percent were in danger of being injured by oncoming traffic, according to the study.

Anecdotal evidence suggests these episodes are all too common. On Oct. 3, a 12-year-old boy who wandered away from his home in Houston died after being struck by a car while trying to cross the freeway.

"We tend to hear about the most traumatic stories on the news," said Dr. Paul Law, director of medical informatics at the Kennedy Krieger Institute in Baltimore, and study researcher. "It's just the tip of the iceberg of what parents are experiencing with this issue."

The more severe symptoms of autism, the more likely the child was to bolt, the study found.

Because the survey was administered through the Interactive Autism Network, a volunteer-based online community through Kennedy Krieger, the study may not provide a clear estimate on the wider number of autistic children who bolt and are at high risk of injury, according to the researchers.

"An unanswered question is whether the risk for elopement is higher in these children because of cognitive issues, their ASD or both," said Dr. Max Wiznitzer, a neurologist at Rainbow Babies & Children's Hospital in Cleveland.

Currently there are no national standards for responding to missing children with autism. The Amber Alert system, which focuses on child abduction, does not cover children with autism who wander.

"Once a child goes missing, there needs to be a way to initiate a search," said Law. "Each minute that goes by without that child being recovered, the chances of a serious outcome goes up tremendously."